KR20210022569A - Bulk boron nitride particles, boron nitride powder, method for producing boron nitride powder, resin composition, and heat dissipation member - Google Patents

Abstract

One aspect of the present disclosure is a bulk boron nitride particle in which primary particles of hexagonal boron nitride are aggregated, wherein the average value of the area ratio of the primary particles in a cross section is 45% or more, and the primary particle in the cross section is The standard deviation of the area ratio of the particles is less than 25, and the crush strength is 8.0 MPa or more.

Description

Bulk boron nitride particles, boron nitride powder, method for producing boron nitride powder, resin composition, and heat dissipation member

The present disclosure relates to a bulk boron nitride particle, a boron nitride powder, a method for producing a boron nitride powder, a resin composition, and a heat dissipating member.

In heat-generating electronic components such as power devices, transistors, thyristors, and CPUs, how to efficiently dissipate heat generated during use becomes an important subject. Conventionally, such heat dissipation measures include (1) high thermal conduction of the insulating layer of a printed wiring board on which a heating electronic component is mounted, or (2) a printed wiring board on which a heating electronic component or a heating electronic component is mounted. It has been generally practiced to mount to a heat sink via an electrically insulating thermal interface material. As the insulating layer and the thermal interface material of the printed wiring board, a resin composition in which ceramic powder is filled with a silicone resin or an epoxy resin is used.

BACKGROUND ART In recent years, with the increase in the speed and integration of circuits in the heat generating electronic parts, and the increase in mounting density of the heat generating electronic parts on the printed wiring board, the heat generation density inside the electronic device is increasing year by year. For this reason, ceramic powders having a higher thermal conductivity than the conventional ones are required.

In the background as described above, hexagonal boron nitride (Hexagonal Boron Nitride) powder, which has excellent properties as an electrical insulating material such as high thermal conductivity, high insulation, and low dielectric constant, is attracting attention.

However, while the hexagonal boron nitride particles have a thermal conductivity of 400 W/(m·K) in the in-plane direction (a-axis direction), the thermal conductivity in the thickness direction (c-axis direction) is 2 W/(m·K). Thus, the anisotropy of the crystal structure and the thermal conductivity derived from the scale phase is large. In addition, when the hexagonal boron nitride powder is filled in a resin, the particles are aligned in the same direction and oriented.

Therefore, for example, in the manufacture of the thermal interface material, the in-plane direction of the hexagonal boron nitride particles (a-axis direction) and the thickness direction of the thermal interface material become perpendicular, and the in-plane direction of the hexagonal boron nitride particles (a-axis direction) ) Was not able to fully utilize the high thermal conductivity.

In Patent Document 1, it is proposed that the in-plane direction (a-axis direction) of the hexagonal boron nitride particles is oriented in the thickness direction of the high heat conduction sheet, and the high thermal conductivity of the hexagonal boron nitride particles in the in-plane direction (a-axis direction) I can save it.

However, in the prior art described in Patent Document 1, (1) it is necessary to laminate the oriented sheet in the next step, so that the manufacturing process is apt to become complicated, and (2) it is necessary to cut thinly into a sheet after lamination and curing. Therefore, there has been a problem that it is difficult to ensure the dimensional accuracy of the thickness of the sheet. Moreover, since the shape of the hexagonal boron nitride particles is scale-like and causes an increase in viscosity and deterioration in fluidity during filling into the resin, high filling of the boron nitride particles into the resin has been difficult.

In order to improve these, various shapes of boron nitride powders having suppressed the anisotropy of the thermal conductivity of hexagonal boron nitride particles have been proposed.

In Patent Document 2, the use of the boron nitride powder in which the hexagonal boron nitride particles of the primary particles are not oriented in the same direction and aggregated is proposed, and it is said that the anisotropy of the thermal conductivity can be suppressed. In addition, as other conventional techniques for producing agglomerated boron nitride, spherical boron nitride produced by spray-drying (Patent Document 3), boron nitride of agglomerates produced using boron carbide (Patent Document 4) as a raw material, and pressing and crushing Agglomerated boron nitride (Patent Document 5) produced by repeating the above is also known. However, in reality, the boron nitride density in the agglomerated particles and the uniformity of the primary particles were not sufficient, and thus, it was not possible to obtain an agglomerated boron nitride having high heat dissipation and insulating properties.

Japanese Unexamined Patent Publication No. 2000-154265 Japanese Laid-Open Patent Publication No. Hei 9-202663 Japanese Unexamined Patent Publication No. 2014-40341 Japanese Unexamined Patent Publication No. 2011-98882 Japanese Patent Publication No. 2007-502770

In the prior art described above, the density of boron nitride contained in the produced agglomerated particles (average value of the ratio of primary particles) cannot be said to be sufficiently high, and since the primary particle structure is not sufficiently uniform, stable high Insulation characteristics and high heat dissipation characteristics could not be solved.

An object of the present disclosure is to provide a bulk boron nitride powder having excellent insulating properties and thermal conductivity. Another object of the present disclosure is to provide a boron nitride powder having excellent insulating properties and thermal conductivity, and a method for producing the same.

As a result of intensive examination, the present inventors found that by a specific production method, the primary particle density of boron nitride contained therein is sufficiently high, and bulk boron nitride particles having a uniform primary structure can be produced. In addition, the inventors of the present invention found out that the above-described bulk boron nitride particles have low anisotropy and high tap density, and that the boron nitride powder containing the bulk boron nitride particles has excellent insulation properties and thermal conductivity, and to complete the present invention. Arrived.

That is, one aspect of the present disclosure may provide the following.

(1) Bulk boron nitride particles in which primary particles of hexagonal boron nitride are aggregated, wherein the average value of the area ratio of the primary particles in the cross section is 45% or more, and the area ratio of the primary particles in the cross section The standard deviation of is less than 25, and the crush strength is 8.0 MPa or more.

(2) The bulk boron nitride particles according to (1), wherein the average value of the area ratio of the primary particles in the cross section is 50 to 85%.

(3) The bulk boron nitride particles according to (1) or (2), wherein the standard deviation of the area ratio of the primary particles in the cross section is 20 or less.

(4) The bulk boron nitride particles according to any one of (1) to (3), wherein the standard deviation of the area ratio of the primary particles in the cross section is 15 or less.

(5) Boron nitride powder containing the bulk boron nitride particles according to any one of (1) to (4).

(6) A boron nitride powder having an average particle diameter of 20 to 100 µm, an orientation index of 12 or less obtained from X-ray diffraction of the powder, and a tap density of 0.85 g/cm 3 or more.

(7) A method for producing boron nitride powder containing bulk boron nitride particles, comprising: a step of calcining boron carbide having a carbon amount of 18.0 to 21.0 mass% in a nitrogen atmosphere of 1800°C or higher and 0.6 MPa or higher to obtain a first calcined product; and The first calcined product is calcined under conditions of an oxygen partial pressure of 20% or more to obtain an oxidation-treated powder, and the oxidation-treated powder and a boron source are mixed, and a liquid component containing boron is vacuum-impregnated into the oxidation-treated powder. And a step of heating and firing the oxidized powder impregnated with the liquid component in a nitrogen atmosphere of 1800° C. or higher to obtain a second calcined product, and a step of pulverizing the second calcined product to pulverize boron nitride containing bulk boron nitride particles. A method for producing boron nitride powder, including a step of obtaining a powder.

(8) A resin composition comprising the boron nitride powder according to (5) or (6) and a resin.

(9) A heat dissipating member containing the cured product of the resin composition according to (8).

According to the present disclosure, it is possible to provide a bulk boron nitride powder excellent in insulation and thermal conductivity. Further, according to the present disclosure, it is possible to provide a boron nitride powder excellent in insulation and thermal conductivity, and a method for producing the same.

1 is a cross-sectional observation photograph of the bulk boron nitride particles of Example 1 by an electron microscope.
2 is a cross-sectional observation photograph of the boron nitride particles of Comparative Example 1 by an electron microscope.

<Bulk boron nitride particles>

The term "bulk boron nitride particles" and "bulk particles" in the present specification refers to nitridation formed by agglomeration of primary particles of scale-shaped hexagonal boron nitride (hereinafter, simply referred to as "primary particles"). It refers to the particles of boron. One embodiment of the bulk boron nitride particles according to the present disclosure is a bulk boron nitride particles in which primary particles of hexagonal boron nitride are agglomerated, and satisfies all of the following conditions (A) to (C).

(A) The average value of the area ratio of the primary particles in the cross section of the bulk boron nitride particles is 45% or more. The average value of the area ratio of the primary particles in the cross section of the bulk boron nitride particles is preferably 50% or more, and more preferably 55% or more. Although there is no upper limit in particular to the average value of this area ratio, it may be less than 90%, 85% or less, or less than 85%, for example. Further, since the bulk boron nitride particles are aggregates of primary particles of boron nitride, it is usually difficult to produce 85% or more bulk boron nitride particles. When the average value of the area ratio described above is less than 45%, there is a tendency that the thermal conductivity of the bulk boron nitride particles decreases due to the coarse internal structure of the bulk boron nitride particles. The average value of the area ratio of the primary particles in the cross section of the bulk boron nitride particles can be adjusted within the above-described range, and may be, for example, 45 to 90% or 50 to 85%.

(B) The standard deviation of the area ratio of the primary particles in the cross section of the bulk boron nitride particles is less than 25. The standard deviation of the area ratio of the primary particles in the cross section of the bulk boron nitride particles is preferably 20 or less, more preferably 15 or less, and still more preferably less than 15. When the above-described standard deviation exceeds 25, the degree of penetration of the resin in each bulk boron nitride particle varies, and when the penetration is insufficient, it causes voids, etc., and the insulation properties (especially, insulation breakdown voltage) are poor. It deteriorates, and the insulation variation also increases with respect to the magnitude|size of a standard deviation. In order to sufficiently penetrate the resin into the bulk boron nitride particles, a method of increasing the press pressure during molding can be considered. However, when the press pressure is excessively increased, the bulk boron nitride particles are disintegrated, the primary particles are oriented, and the thermal conductivity is lowered.

The average value and the standard deviation of the "area ratio of primary particles in a cross-section" of the bulk boron nitride particles in the present specification mean values determined by the method described in Examples.

(C) The crush strength is 8.0 MPa or more. The crushing strength of the bulk boron nitride particles is preferably 10.0 MPa or more, and more preferably 12.0 MPa or more. When the crushing strength is less than 8.0 MPa, a problem occurs in that the bulk boron nitride particles are collapsed due to stress during kneading or pressing with a resin, resulting in a decrease in thermal conductivity. "Crushing strength" in this specification means the crushing strength (single granule crushing strength) determined in accordance with JIS R1639-5:2007.

When the crushing strength of the bulk boron nitride particles is 8.0 MPa or more, it is possible to reduce the destruction of the bulk boron nitride particles in a pulverization step, a manufacturing step of a heat dissipating member, and the like. For this reason, the boron nitride powder containing this bulky boron nitride particle can be used suitably for a heat dissipating member. In addition, the upper limit of the crushing strength of the bulk boron nitride particles is not particularly limited, but it can be produced so as to be, for example, 30 MPa or less, or 20 MPa or less.

The aspect ratio (ratio of long diameter and thickness: length/thickness of long diameter) of the primary particles constituting the bulk boron nitride particles is preferably 11 to 18, more preferably 12 to 15. When the aspect ratio is 11 or more, the thermal conductivity can be further improved. When the aspect ratio is 18 or less, a decrease in crush strength can be more sufficiently suppressed. The aspect ratio of the primary particles can be obtained from an electron micrograph of the bulk boron nitride particles, and is specifically determined by the method described in Examples.

<Boron nitride powder>

One embodiment of the boron nitride powder according to the present disclosure is a boron nitride powder containing the above-described bulk boron nitride particles. That is, the boron nitride powder includes bulk boron nitride particles in which primary particles of the scale-shaped hexagonal boron nitride are agglomerated. The boron nitride powder preferably further satisfies all of the following conditions (D) to (F).

(D) The average particle diameter of the boron nitride powder is 20 to 100 µm. The average particle diameter of the boron nitride powder is 20 µm or more, more preferably 25 µm or more, and still more preferably 30 µm or more. Moreover, the average particle diameter of the boron nitride powder is 100 micrometers or less, More preferably, it is 90 micrometers or less, More preferably, it is 80 micrometers or less. The range of the average particle diameter of the boron nitride powder can be adjusted within the range of 20 to 100 µm, preferably 25 to 90 µm.

When the average particle diameter of the boron nitride powder is too small to be less than 20 µm, a problem of lowering the thermal conductivity may occur. In addition, when the average particle diameter of the boron nitride powder exceeds 100 µm and is too large, the difference between the thickness of the sheet and the average particle diameter of the boron nitride powder decreases, and thus the sheet may be difficult to manufacture.

(E) The orientation index obtained from powder X-ray diffraction of the boron nitride powder is 12 or less. The orientation index of the boron nitride powder is 12 or less, preferably 10 or less, and more preferably 8 or less. The higher the abundance ratio of the bulk boron nitride particles in which the primary particles are not substantially oriented in the bulk boron nitride powder, the smaller the orientation index of the boron nitride powder. When the orientation index of the boron nitride powder exceeds 12 and is too large, that is, it suggests that there are many single particles that are not aggregated, a problem of lowering the thermal conductivity arises. The lower limit of the orientation index of the boron nitride powder is not particularly limited, but it is generally considered to be a value of about 6.7 even when completely random.

The "orientation index" in this specification means the peak intensity ratio [I(002)/I(100)] of the (002) plane and the (100) plane measured using an X-ray diffraction apparatus, and specifically Is determined by the method described in Examples.

(F) The tap density of the boron nitride powder is 0.85 g/cm 3 or more. The tap density of the boron nitride powder is 0.85 g/cm 3 or more, more preferably 0.90 g/cm 3 or more. When the tap density of the boron nitride powder is less than 0.85 g/cm 3, the percolation between the bulk boron nitride particles is not sufficient, resulting in a problem of lowering the thermal conductivity. The upper limit of the tap density of the boron nitride powder is not particularly limited, but considering the theoretical density of boron nitride (2.26 g/cm 3 ), the practical upper limit is considered to be a value of about 1.5 g/cm 3.

The "tap density" in this specification means a value obtained in accordance with JIS R 1628:1997, and specifically, it is determined by the method described in Examples.

Another embodiment of the boron nitride powder according to the present disclosure is a novel boron nitride powder that satisfies all the conditions of the above (D) to (F). This boron nitride powder preferably contains the above-described bulk boron nitride particles.

The thermal conductivity of the boron nitride powder according to the present disclosure can be, for example, 10 W/(m·K) or more. In addition, when the boron nitride powder according to the present disclosure evaluates the dielectric breakdown property on a plurality of evaluation samples prepared by containing it, the ratio of the evaluation samples that undergo dielectric breakdown under a voltage of 40 kV/mm is 5% or less. can do. Thus, the boron nitride powder according to the present disclosure has both high thermal conductivity and high dielectric breakdown voltage. Therefore, the boron nitride powder can be preferably used as a heat dissipating member for heat-generating electronic parts (electronic parts accompanying heat generation) such as power devices, and particularly, can be preferably used as a raw material for forming a thin-film heat dissipating member. .

<Production method of boron nitride powder containing bulk boron nitride particles>

One embodiment of the boron nitride powder containing the bulk boron nitride particles according to the present invention is a method for producing a boron nitride powder containing the bulk boron nitride particles, wherein the boron carbide having a carbon amount of 18.0 to 21.0 mass% is 1800°C or higher. Further, a step of firing in a nitrogen atmosphere of 0.6 MPa or more to obtain a first fired product (first step), and a step of firing the first fired product under conditions of an oxygen partial pressure of 20% or more to obtain an oxidized powder (second step) And, a step of mixing the oxidation treatment powder and a boron source, and vacuum impregnation of the oxidation treatment powder with a liquid component containing boron (third step); and a step of impregnating the oxidation treatment powder with the liquid component at 1800°C or higher. Heating and firing in a nitrogen atmosphere to obtain a second fired product (fourth process), and a process of pulverizing the second fired product to obtain boron nitride powder containing bulk boron nitride particles (a fifth process). The method for producing the boron nitride powder can also be referred to as a method for producing the bulk boron nitride particles, since the above-described bulk boron nitride particles are prepared. Each of the first to fifth steps will be described below.

[First step: pressurized nitriding firing step]

In the first step, boron carbonitride is obtained by firing a specific boron carbide in a nitrogen atmosphere under a specific calcination temperature and a specific pressurization condition. The first step is, for example, a step of calcining boron carbide having a carbon amount of 18.0 to 21.0% by mass in a nitrogen atmosphere of 1800°C or higher and 0.6 MPa or higher to obtain a first calcined product. The first fired product contains boron carbonitride, preferably boron carbonitride.

(Boron carbide used in the first step)

It is preferable that the carbon amount of boron carbide is lower than 21.7 mass% of the theoretical amount calculated from the _{composition formula B 4 C.} The carbon amount of boron carbide should just be in the range of 18.0-21.0 mass %. The lower limit of the carbon amount of boron carbide is preferably 19% by mass or more. The upper limit of the carbon amount of boron carbide is preferably 20.5% by mass or less. If the carbon amount of boron carbide exceeds 21% by mass and is too large, the amount of carbon volatilized during the second step to be described later becomes too large, and it is not possible to produce dense bulk boron nitride particles, and the carbon amount of boron nitride finally produced is excessive. It is not preferable because there are many problems. In addition, it is usually difficult to produce a stable boron carbide in which the carbon amount of boron carbide is less than 18.0 mass% because the deviation from the theoretical composition is too large.

It is preferable that boron carbide does not contain impurity boric acid or free carbon except inevitable, or even if it is contained in a small amount.

The average particle diameter of boron carbide may be, for example, 8 to 60 µm in consideration of the influence of the average particle diameter of the finally obtained bulk boron nitride particles. The average particle diameter of boron carbide is preferably 8 µm or more, and more preferably 10 µm or more. When the average particle diameter of boron carbide is 8 µm or more, an increase in the orientation index of the resulting boron nitride powder can be sufficiently suppressed. The upper limit of the average particle diameter of boron carbide is preferably 60 µm or less, more preferably 50 µm or less. When the average particle diameter of the boron carbide is 60 µm or less, the growth of the bulk boron nitride particles can be made appropriate, and generation of coarse particles can be suppressed.

As the boron carbide, a commercially available one may be used, or a separately prepared one may be used. As a preparation method in the case of preparing boron carbide, a known preparation method can be applied, and boron carbide having a desired average particle diameter and carbon amount can be obtained.

As a method for preparing boron carbide, for example, after mixing boric acid and acetylene black, heating in an inert gas atmosphere at 1800 to 2400°C for 1 to 10 hours to obtain a boron carbide lump is mentioned. In the above preparation method, the obtained boron carbide lump may be appropriately subjected to, for example, pulverizing, sieving, washing, removing impurities, and drying.

In the mixing of boric acid and acetylene black, which is a raw material for boron carbide, it is preferable that the amount of acetylene black is, for example, 25 to 40 parts by mass based on 100 parts by mass of boric acid.

The atmosphere when preparing boron carbide is preferably an inert gas. Examples of the inert gas include argon gas and nitrogen gas. The inert gas can be used alone or in combination with argon gas and nitrogen gas. Among the gases, the inert gas is preferably argon gas.

In the case of pulverizing the boron carbide lump, a general pulverizer or pulverizer can be used. The pulverization time of the boron carbide lump may be, for example, about 0.5 to 3 hours. When the pulverization time of the boron carbide lump is within the above range, boron carbide having an appropriate particle diameter can be obtained. The boron carbide after pulverization is preferably sieved to a particle diameter of 75 µm or less using a sieve, for example.

(Various conditions in the first step)

The firing temperature in the first step is 1800°C or higher, preferably 1900°C or higher. Moreover, the upper limit of the firing temperature in the first step is 2400°C or less, and preferably 2200°C or less. The firing temperature in the first step can be adjusted within the above-described range, and may be, for example, 1800 to 2200°C.

The pressure in the first step is preferably 0.6 MPa or more, and more preferably 0.7 MPa or more. Moreover, the upper limit of the pressure in a 1st process becomes like this. Preferably it is 1.0 MPa or less, More preferably, it is 0.9 MPa or less. The pressure in the first step can be adjusted within the above-described range, and may be, for example, 0.7 to 1.0 MPa. When the said pressure is 0.6 MPa or more, nitriding of boron carbide can be advanced more fully. Further, from the viewpoint of cost, the pressure is preferably 1.0 MPa or less, but it is also possible to set the pressure to a value higher than this.

The firing temperature and pressure conditions in the first step are preferably from 1800 to 2200°C and from 0.7 to 1.0 MPa of the firing temperature. When the firing temperature is 1800°C and the pressure is less than 0.7 MPa, the nitridation of boron carbide may not proceed sufficiently.

The atmosphere in the first step is a gas atmosphere in which the nitridation reaction of boron carbide proceeds. Examples of the atmosphere in the first step include nitrogen gas and ammonia gas. Nitrogen gas, ammonia gas, and the like can be used alone or in combination of two or more. As the atmosphere in the first step, nitrogen gas is preferable in view of ease of nitriding and cost. The content of the nitrogen gas in the atmosphere in the first step is preferably 95% (V/V) or more, and more preferably 99.9% (V/V) or more.

The firing time in the first step is not particularly limited as long as the nitriding proceeds sufficiently. The firing time in the first step is preferably 6 to 30 hours, more preferably 8 to 20 hours.

[Second step: oxidation treatment step]

In the second step, the boron carbonitride obtained in the first step is heat-treated under a specific atmosphere to obtain boron carbonitride having a low carbon amount. The second step is, for example, a step of firing the first fired product described above under conditions in which oxygen partial pressure is 20% or more to obtain an oxidized powder. The oxidation treatment powder contains boron carbonitride (boron carbonitride having a low carbon amount) with a lower carbon amount than boron carbonitride obtained in the first step, and is preferably boron carbonitride having a low carbon amount.

In the second step, more specifically, the boron carbonitride obtained in the first step is subjected to a heat treatment in which the boron carbonitride obtained in the first step is kept in a specific temperature range described later for a certain period of time under an oxygen partial pressure atmosphere of 20% or more. A step of obtaining low-carbon boron carbonitride particles by oxidizing and decarburizing a small amount may be sufficient. That is, the second process can be referred to as a decarburization crystallization process, and it contains boron while making voids inside by decarbonizing boron carbonitride, making it easier to impregnate the liquid component containing boron used in the subsequent process. It is possible to reduce the amount of the liquid component used.

The oxygen partial pressure in the second step is 20% or more, preferably 30% or more with respect to the voltage. Decarburization can be performed at low temperatures by treating boron carbonitride under conditions where the oxygen partial pressure is higher than that of the atmosphere. Further, since the oxidation treatment of boron carbonitride can be performed at a low temperature, excessive oxidation of boron carbonitride itself can be prevented.

The upper limit of the heating temperature (oxidation temperature) in the second step is preferably 950°C or less, and more preferably 900°C or less. Moreover, the lower limit of the heating temperature in the second step is preferably 450°C or higher, and more preferably 500°C or higher. When the heating temperature is 450° C. or higher, the decarburization of boron carbonitride can be more sufficiently advanced. When the heating temperature is 950°C or less, oxidation of boron carbonitride itself can be more sufficiently suppressed.

The firing time in the second step is not particularly limited as long as the oxidation proceeds sufficiently. The firing time in the second step is preferably 3 to 25 hours, more preferably 5 to 20 hours.

[3rd process: impregnation treatment process]

In the third step, the low-carbon boron carbonitride obtained in the second step is mixed with a component containing boron serving as a boron source, and then a liquid component containing boron is impregnated. The third step is, for example, a step of mixing the oxidized powder and a boron source, and vacuum impregnating the oxidized powder with a liquid component containing boron.

In the third step, more specifically, after mixing the low-carbon boron carbonitride obtained in the second step with a component containing boron serving as a boron source, it is maintained for a certain period of time in a specific temperature range described later in a vacuum atmosphere. It may be a step of obtaining a mixture obtained by impregnating a liquid component containing boron and a low carbon amount of boron carbonitride uniformly and impregnating the liquid component containing boron in the voids in the low carbon amount of boron carbonitride by performing the heat treatment.

In the third step, as a raw material, a boron source is mixed with the low-carbon boron carbonitride obtained in the second step, and further decarburization crystallization is performed. Examples of the boron source include boric acid and boron oxide. The boron source can be used alone or in combination with boric acid and boric acid oxide. In the third step, in addition to the low-carbon amount of boron carbonitride and the boron source, if necessary, an additive used in the technical field may be further mixed.

The mixing ratio of the boron carbonitride and the boron source can be appropriately set depending on the molar ratio. When using boric acid or boron oxide as the boron source, the total blending amount of boric acid and boron oxide is based on 100 parts by mass of boron carbonitride, for example, preferably 10 to 100 parts by mass, more preferably It is 20 to 80 parts by mass. Moreover, you may mix an auxiliary agent as needed. As an auxiliary agent, sodium carbonate etc. are mentioned, for example.

The firing temperature in the third step is not particularly limited as long as the impregnation proceeds sufficiently. The firing temperature in the third step is preferably 200 to 500°C, more preferably 250 to 450°C, and still more preferably 300 to 400°C. When the firing temperature in the third step is 200°C or higher, the liquid component containing boron can be more sufficiently impregnated in boron carbonitride. When the firing temperature in the third step is 500°C or less, volatilization of the liquid component containing boron can be suppressed.

The degree of vacuum in the third step is preferably 1 to 1000 Pa. The treatment time in the third step is preferably from 10 minutes to 2 hours, more preferably from 20 minutes to 1 hour. Moreover, although it is preferable to perform the 3rd process and the 4th process mentioned later in relation to cost continuously, it does not matter even if it implements each separately.

[4th process: crystallization process]

In the fourth step, the mixture of the boron-containing liquid component obtained in the third step and the low-carbon boron carbonitride is heated and fired in a nitrogen atmosphere to obtain a second fired product. The 4th process is a process of obtaining a 2nd fired product by heat-baking in a nitrogen atmosphere of 1800 degreeC or more.

In the fourth step, more specifically, a mixture of a liquid component containing boron obtained in the third step and a low-carbon boron carbonitride mixture is heated in a nitrogen atmosphere of a normal pressure or higher until the holding temperature is reached at a specific temperature rising rate. By carrying out heat treatment and holding it in a specific temperature range for a certain period of time, it is possible to obtain bulk boron nitride particles in which primary particles are agglomerated to form a lump and aggregates thereof. That is, in the fourth step, boron carbonitride is crystallized to form scales of a predetermined size, and these can be uniformly agglomerated to obtain bulk boron nitride particles.

The pressure of the nitrogen atmosphere in the fourth step may be normal pressure (atmospheric pressure) or may be pressurized. The pressure of the nitrogen atmosphere in the case of pressurization is, for example, preferably 0.5 MPa or less, and more preferably 0.3 MPa or less.

In the 4th process, you may adjust the temperature increase rate at the time of reaching the holding|maintenance temperature of baking. The rate of temperature increase when heating up to the holding temperature in the fourth step is, for example, preferably 5°C/min (that is, Celsius degree per minute) or less, and more preferably 4°C/min or less, It is more preferably 3° C./min or less, and even more preferably 2° C./min or less.

The holding temperature after the above-described temperature rise is 1800°C or higher, preferably 2000°C or higher. In addition, the upper limit of the holding temperature is not particularly limited, but is preferably 2200°C or less, and more preferably 2100°C or less. If the holding temperature is too low (below 1800°C), grain growth does not occur sufficiently, and the thermal conductivity of the boron nitride powder may be lowered. On the other hand, when the holding temperature is 1800°C or higher, grain growth is likely to occur favorably, and the effect that the thermal conductivity is easily improved is obtained.

The holding time at the holding temperature is not particularly limited as long as crystallization proceeds sufficiently. The holding time at the holding temperature is preferably more than 0.5 hours, more preferably 1 hour or more, still more preferably 3 hours or more, even more preferably 5 hours or more, and even more preferably 10 It's more than an hour. Moreover, the upper limit of the holding time becomes like this. Preferably it is less than 40 hours, More preferably, it is 30 hours or less, More preferably, it is 20 hours or less. When the holding time exceeds 0.5 hours, it is expected that grain growth will occur satisfactorily. In addition, if the holding time is less than 40 hours, it can be expected that grain growth proceeds excessively and the crush strength decreases, and also industrially disadvantageous due to a longer firing time can be expected to be reduced. The holding time at the holding temperature can be adjusted within the above-described range, preferably more than 0.5 hours and less than 40 hours, and more preferably 1 to 30 hours.

[Fifth process: grinding process]

In the fifth step, the second fired product prepared in the fourth step is pulverized to adjust the particle size. The fourth step is, for example, a step of pulverizing the above-described second fired product to obtain boron nitride powder containing bulk boron nitride particles. For pulverization, a general pulverizer or pulverizer can be used. Examples of the crusher or crusher include a ball mill, a vibration mill, and a jet mill. In addition, "pulverization" in this specification shall also include "disintegration".

<Resin composition: Thermally conductive resin composition>

One embodiment of the resin composition according to the present disclosure contains a resin and the above-described boron nitride powder. The resin composition is also referred to as a thermally conductive resin composition because it can exhibit thermal conductivity. The heat conductive resin composition can be prepared, for example, by the following method. The preparation method of the thermally conductive resin composition has, for example, a step of mixing the above-described boron nitride powder with a resin. For the preparation method of this thermally conductive resin composition, a known method for producing a resin composition can be used. The obtained thermally conductive resin composition can be widely used, for example, in a heat dissipating member or the like.

(Suzy)

Examples of resins used in the thermally conductive resin composition include epoxy resins, silicone resins, silicone rubbers, acrylic resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, cyanate resins, benzoxazine resins, and fluorine resins. , Polyamide, polyimide (e.g., polyimide, polyamideimide, polyetherimide, etc.), polyester (e.g., polybutylene terephthalate, polyethylene terephthalate, etc.), polyphenylene ether, polyphenyl Rensulfide, wholly aromatic polyester, polysulfone, polyethersulfone, liquid crystal polymer, polycarbonate, maleimide modified resin, ABS resin, AAS resin (acrylonitrile-acrylic rubber/styrene resin), AES resin (acrylonitrile Ethylene/propylene/diene rubber-styrene resin), etc. can be used.

The resin is particularly preferably an epoxy resin (preferably a naphthalene-type epoxy resin) or a silicone resin. The heat conductive resin composition containing an epoxy resin is preferable as an insulating layer of a printed wiring board from the viewpoint of excellent heat resistance and adhesive strength to a copper foil circuit. Further, a heat conductive resin composition containing a silicone resin is preferable as a thermal interface material from the viewpoint of excellent heat resistance, flexibility, and adhesion to a heat sink.

Specific examples of the curing agent in the case of using an epoxy resin include a phenol novolak resin, an acid anhydride resin, an amino resin, and imidazoles. Among these, the curing agent is preferably imidazoles. The blending amount of this curing agent is preferably 0.5 to 15 parts by mass, more preferably 1.0 to 10 parts by mass with respect to 100 parts by mass of the raw material (monomer).

The content of the boron nitride powder is preferably 30 to 85% by volume, and more preferably 40 to 80% by volume based on 100% by volume of the thermally conductive resin composition. When the content of the boron nitride powder is 30% by volume or more, the thermal conductivity can be further improved, and more sufficient heat dissipation performance is likely to be obtained. Moreover, when the content of the boron nitride powder is 85% by volume or less, it is possible to reduce the occurrence of voids and the like during molding into a heat dissipating member or the like, and further reduce the decrease in insulation properties and mechanical strength.

<heat radiating member>

One embodiment of the heat dissipation member is a member using the resin composition (thermal conductive resin composition) described above. The heat dissipation member preferably contains the cured product of the resin composition described above.

As described above, several embodiments have been described, but the present disclosure is not limited to the above embodiments at all. In addition, the description of the above-described embodiment can be applied to each other.

Example

Hereinafter, the present disclosure will be described in detail with reference to Examples and Comparative Examples. In addition, the present disclosure is not limited to the following examples.

Various measurement methods are as follows.

(1) The average value and standard deviation of the area ratio of the primary particles in the cross section of the bulk boron nitride particles

The average value and standard deviation of the area ratio of the primary particles (boron nitride particles) in the cross section of the bulk boron nitride particles were measured as follows. First, for the produced bulk boron nitride powder, as a pretreatment for observation, bulk boron nitride particles were embedded with an epoxy resin. Next, it was subjected to cross-section exposure processing by the CP (cross section polisher) method and fixed to the sample stand. After fixing, osmium coating of the cross-section was performed.

The cross-sectional observation was performed using a scanning electron microscope (manufactured by Nippon Electronics Co., Ltd., "JSM-6010LA") at an observation magnification: 2000 to 5000 times. The cross-sectional image of the obtained bulk boron nitride particles is input into image analysis software (manufactured by Mountek Co., Ltd., "Mac-view"), and the primary in an arbitrary 10 µm × 10 µm area in the cross-sectional image of the bulk boron nitride particles The area ratio of the particles (boron nitride particles) was calculated. Similarly, the area ratio of the primary particles was calculated at a point of 50 visual fields or more, and the average value was taken as the average value of the area ratio of the primary particles. By the same method, the standard deviation of the area ratio of the primary particles was calculated, and the value was taken as the standard deviation of the area ratio of the primary particles. Fig. 1 shows a SEM image of a cross section of the bulk boron nitride prepared in Example 1.

Further, as a parameter indicating the internal structure of the bulk boron nitride particles, there is a measurement of pore size distribution by a mercury porosimeter or the like. However, in the results obtained by measuring the pore diameter distribution of a powder, which is an aggregate of aggregated particles such as bulk boron nitride particles, it is difficult to clearly distinguish between the aggregated particles and the inside of the aggregated particles. In addition, there is a possibility that the agglomerated particles themselves may collapse during the pore diameter distribution measurement, and this does not necessarily match the result of electron microscopic observation of the agglomerated particle cross section. In addition, the result obtained by the pore diameter distribution measurement as described above and the insulating property and heat dissipation property of the boron nitride powder obtained are not necessarily correlated. Therefore, in the present disclosure, an evaluation method based on image analysis is employed as described above.

(2) crush strength of bulk boron nitride particles

The crush strength was measured according to JIS R1639-5:2007. As a measuring device, a micro compression tester (manufactured by Shimadzu Corporation, "MCT-W500") was used. The crush strength (σ: unit ㎫) is from the dimensionless number (α = 2.48) that varies depending on the position in the particle, the crush test force (P: unit N) and the particle diameter (d: unit µm), σ = α × P/( It is a value calculated using the formula of π × d ^{2 ).} Specifically, the same measurement was performed for 20 particles or more by changing the particles, and the average value was taken as the crush strength.

(3) aspect ratio of primary particles

The aspect ratio (ratio of long diameter and thickness: length/thickness of long diameter) of the scale-shaped hexagonal boron nitride primary particles was carried out in accordance with the method of Japanese Unexamined Patent Application Publication No. 2007-308360. Specifically, from the electron micrograph of the surface of the bulk boron nitride particles, 100 or more primary particles in which the major diameter (total length) and thickness of the primary particles are confirmed were selected, and the major diameter and thickness were measured. The ratio of the long diameter to the thickness was calculated from the measurement result, and the average value was taken as the aspect ratio of the primary particles.

(4) Average particle diameter of boron nitride powder

The average particle diameter of the boron nitride powder was measured in accordance with ISO 13320:2009, using a laser diffraction scattering method particle size distribution measuring device (manufactured by Beckman Coulter Co., Ltd., "LS-13 320"). However, it was measured without passing a homogenizer through the sample before the measurement treatment. This average particle diameter is a particle diameter (median diameter, d50) of 50% of the cumulative value of the cumulative particle size distribution. In the particle size distribution measurement, water was used as a solvent for dispersing the aggregate, and hexametaphosphoric acid was used as a dispersant. At this time, 1.33 was used for the refractive index of water, and a numerical value of 1.80 was used for the refractive index of boron nitride powder.

(5) Orientation index of boron nitride powder

The orientation index of the boron nitride powder was measured using an X-ray diffraction apparatus (manufactured by Rigaku Co., Ltd., "ULTIMA-IV"). A sample was prepared by hardening boron nitride powder on the attached glass cell, and the sample was irradiated with X-rays to calculate the peak intensity ratio [I(002)/I(100)] of the (002) plane and the (100) plane. And evaluated this as an orientation index.

(6) Tap density of boron nitride powder

The tap density of the boron nitride powder was measured according to JIS R 1628:1997. For the measurement, a commercially available device can be used. Specifically, the boron nitride powder was filled in a 100 cm 3 dedicated container, and the bulk density after tapping was performed under the conditions of a tapping time of 180 seconds, a tapping frequency of 180 times, and a tap lift of 18 mm, and the obtained value as a tap density. I did.

(7) Thermal conductivity

The thermal conductivity was measured using a sheet produced from a thermally conductive resin composition containing boron nitride powder as a measurement sample. Thermal conductivity (H: unit W/(m·K)) is the thermal diffusivity (A: unit m²/sec), density (B: unit kg/m3), and specific heat capacity (C: unit J/(kg·K)) ), it was calculated based on the formula of H=A×B×C.

The thermal diffusivity (A) prepared a sample obtained by processing the above-described sheet into a width of 10 mm x 10 mm x a thickness of 0.3 mm, and was determined by a laser flash method targeting this. As a measuring device, a xenon flash analyzer (manufactured by NETZSCH, "LFA 447 NanoFlash") was used. The density (B) was calculated|required using the Archimedes method. The specific heat capacity (C) was calculated|required using DSC (manufactured by Rigaku Co., Ltd., "ThermoPlusEvo DSC8230"). The pass value of the thermal conductivity was set to 10 W/(m·K) or more, and 12 W/(m·K) or more was made excellent.

(8) Insulation: insulation breakdown voltage

The dielectric breakdown voltage of the produced substrate was measured in accordance with JIS C 6481:1996, using a withstand voltage tester (manufactured by Kikusui Electronics Co., Ltd., "TOS 8650"). Measurement was carried out for 100 samples. When the thickness of the cured layer of the resin composition containing boron nitride powder is 200 µm, the proportion of the sample causing dielectric breakdown when a voltage of 40 kV/mm is applied is 5% or less as "A (pass)", 5 to What was 20% was evaluated as "B", and what was 20% or more was evaluated as "C (disqualification)".

(9) Measurement of carbon content of boron carbide

The carbon amount of boron carbide was measured using a carbon analyzer (manufactured by LECO, "IR-412 type").

[Example 1]

In Example 1, as shown below, boron nitride powder was produced. The produced boron nitride powder was filled into the resin and evaluated.

(Boron carbide synthesis)

After mixing 100 parts by mass of boric acid (manufactured by Nippon Denko Corporation, orthoboric acid) and 35 parts by mass of acetylene black (manufactured by Denka Corporation, trade name: HS100) with a Henschel mixer, the obtained mixture was charged into a graphite crucible. Thereafter, using an arc furnace, the mixture was heated for 5 hours under conditions of an argon atmosphere and 2200°C to synthesize _{boron carbide (B 4 C).}

The synthesized boron carbide lump was pulverized for 1 hour with a ball mill, and then sieved to a particle size of 75 µm or less using a sieve. Thereafter, boron carbide was further washed with an aqueous nitric acid solution to remove impurities such as iron powder, filtered and dried to prepare boron carbide powder having an average particle diameter of 20 µm. The carbon content of the obtained boron carbide powder was 20.0 mass%.

(Step 1)

After filling the synthesized boron carbide into a crucible made of boron nitride, boron nitride is heated for 10 hours under a nitrogen gas atmosphere, 2000°C, and 9 atm (0.8 MPa) using a resistance heating furnace. (B ₄ CN ₄ ) was prepared. The carbon amount of the obtained boron carbonitride was 9.9 mass %.

(Second process)

After filling the synthesized boron carbonitride into a crucible made of alumina, using a muffle furnace, by heating boron carbonitride for 5 hours under conditions of an atmosphere of 40% oxygen partial pressure and 700°C, in the first step described above. Boron carbonitride having a lower carbon amount than the obtained boron carbonitride was obtained. The carbon content of the low-carbon boron carbonitride was 2.5% by mass.

(3rd process)

After mixing 100 parts by mass of the synthesized boron carbonitride and 45 parts by mass of boric acid using a Henschel mixer, the obtained mixture was charged into a crucible made of boron nitride. Thereafter, the mixture was held for 1 hour under the conditions of a vacuum atmosphere of 100 Pa and 420°C using a resistance heating furnace.

(4th process)

Subsequent to the impregnation treatment step in vacuum, nitrogen gas was introduced into the resistance heating furnace, and the temperature was raised from room temperature to 1000°C at a temperature increase rate of 10°C/min under conditions of 0.3 MPa and nitrogen gas atmosphere, and then the temperature increase rate. Was changed to 2°C/min, and the temperature was raised from 1000°C to 2000°C. The above-described mixture was further heated at the holding temperature of 2000°C and the holding time was 5 hours, whereby the primary particles were agglomerated to synthesize an aggregate of bulk boron nitride particles that became lumps.

(The fifth step)

The aggregate of the synthesized bulk boron nitride particles was pulverized using a Henschel mixer, and then classified into a nylon sieve having a sieve mesh of 100 µm using a sieve, thereby producing a boron nitride powder having an average particle diameter of 45 µm. The obtained boron nitride powder had a porosity of 48% and a specific surface area of 4.2 m 2 /g. In addition, the porosity was determined by measuring the total pore volume using a mercury porosimeter in accordance with JIS R 1655.

(Preparation of resin composition: filling into resin)

The properties of the obtained boron nitride powder as a filler for resin were evaluated. A mixture of 100 parts by mass of a naphthalene-type epoxy resin (manufactured by DIC Corporation, brand name: HP4032) and 10 parts by mass of a curing agent (manufactured by Shikoku Chemical Industry Co., Ltd., imidazoles, brand name: 2E4MZ-CN) was prepared. The mixture was 100% by volume, and boron nitride powder was further mixed so that the boron nitride powder was 50% by volume to prepare a slurry. The slurry was applied on a PET sheet to a thickness of 0.3 mm to form a coating film. Thereafter, vacuum degassing of the coating film was performed for 10 minutes under a reduced pressure of 500 Pa. Subsequently, under the conditions of a temperature of 150°C and a pressure of 160 kg/cm 2, the coating film was press-heated and pressurized over 60 minutes to form a sheet having a thickness of 0.3 mm.

In Table 1 and Table 2 below, the measurement values and evaluation results were shown together with other Examples and Comparative Examples.

[Example 2]

In Example 2, a boron nitride powder was produced in the same manner as in Example 1 except that the pulverization time at the time of preparing boron carbide was changed to 30 minutes, and "boron carbide having an average particle diameter of 40 µm" was prepared.

[Example 3]

In Example 3, a boron nitride powder was prepared in the same manner as in Example 1 except that the pulverization time at the time of preparing boron carbide was changed to 1.5 hours, and "boron carbide having an average particle diameter of 12 µm" was prepared.

[Example 4]

Example 4 was carried out in the same manner as in Example 1 except that the holding time in the second step was changed to 9 hours to obtain ``a low carbon amount of boron carbonitride (carbon amount: 0.8% by mass)'', and boron nitride powder Was prepared.

[Example 5]

Example 5 was carried out in the same manner as in Example 1 except that the holding time in the second step was changed to 0.5 hours to obtain ``a low carbon amount of boron carbonitride (carbon amount: 4.5% by mass)'', and boron nitride powder Was prepared.

[Example 6]

Example 6 was carried out in the same manner as in Example 1, except that the firing temperature in the third step was changed to 200°C, and boron nitride powder was produced.

[Example 7]

Example 7 was carried out in the same manner as in Example 1, except that the firing temperature in the third step was changed to 350°C, and boron nitride powder was produced.

[Comparative Example 1 and Comparative Example 2]

About the two types of commercially available boron nitride powders (commercial products a and b), it evaluated similarly to Examples 1-7. The results of the commercial product a are shown in the table as Comparative Example 1 and the results of the commercial product b are shown as Comparative Example 2. Further, an SEM image of Comparative Example 1 is shown in FIG. 2. The boron nitride powder in Comparative Example 1 had a porosity of 38% and a specific surface area of 3.2 m 2 /g.

[Comparative Example 3]

In Comparative Example 3, 100 parts by mass of boron carbonitride and 200 parts by mass of boric acid were mixed using a Henschel mixer before the fourth step, without performing the second step and the third step, and the resulting mixture was charged into a boron nitride crucible. A boron nitride powder was prepared in the same manner as in Example 1 except for the one.

Industrial applicability

The present disclosure can provide boron nitride powder having excellent thermal conductivity and dielectric breakdown properties, and a method for producing the same. The boron nitride powder can be blended into a resin composition, and can be used, for example, by filling an insulating layer of a printed wiring board and a resin composition of a thermal interface material. The resin composition may be cured and used. The resin composition containing the boron nitride powder of the present disclosure and the cured product thereof can be used, for example, in a heating member or the like. This heat dissipation member can be widely used, and can be used, for example, as a heat dissipation member of an electronic component accompanying heat generation such as a power device.

Claims (9)

As the bulk boron nitride particles in which primary particles of hexagonal boron nitride are agglomerated,
The average value of the area ratio of the primary particles in the cross section is 45% or more,
The standard deviation of the area ratio of the primary particles in the cross section is less than 25,
Bulk boron nitride particles having a crush strength of 8.0 MPa or more. The method of claim 1,
The bulk boron nitride particles, wherein the average value of the area ratio of the primary particles in the cross section is 50 to 85%. The method according to claim 1 or 2,
The bulk boron nitride particles, wherein the standard deviation of the area ratio of the primary particles in the cross section is 20 or less. The method according to any one of claims 1 to 3,
The bulk boron nitride particles, wherein the standard deviation of the area ratio of the primary particles in the cross section is 15 or less. The boron nitride powder containing the bulk boron nitride particle of any one of Claims 1-4. A boron nitride powder having an average particle diameter of 20 to 100 µm, an orientation index obtained from powder X-ray diffraction of 12 or less, and a tap density of 0.85 g/cm 3 or more. As a method for producing boron nitride powder containing bulk boron nitride particles,
A step of calcining boron carbide having a carbon amount of 18.0 to 21.0% by mass in a nitrogen atmosphere of 1800°C or higher and 0.6 MPa or higher to obtain a first fired product;
A step of firing the first fired product under conditions of an oxygen partial pressure of 20% or more to obtain an oxidized powder;
A step of mixing the oxidized powder and a boron source, and vacuum impregnating the oxidized powder with a liquid component containing boron;
A step of heating and firing the oxidation-treated powder impregnated with the liquid component in a nitrogen atmosphere of 1800° C. or higher to obtain a second fired product; and
A method for producing boron nitride powder, comprising a step of pulverizing the second calcined product to obtain boron nitride powder including bulk boron nitride powder. A resin composition comprising the boron nitride powder according to claim 5 or 6 and a resin. A heat dissipating member comprising a cured product of the resin composition according to claim 8.

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